Voters in the southern German heartland of Bavaria dealt a stinging blow to Chancellor Angela Merkel's conservative allies.
The projected result, if confirmed, marks a humbling moment for the Christian Social Union, a party that has governed for decades, while boosting the fortunes of players to both the left and the right in an election defined by polarised opinions about immigration.
Votes for the Bavarian state parliament have rarely been competitive in modern lifetimes. The CSU has been a juggernaut of postwar Bavaria, leading the region for 61 consecutive years and rarely needing a partner to do so.
The party is expected to continue to govern even after Sunday's election. But projected results based on exit polls showed the CSU's share of the vote falling dramatically, from nearly half in 2013 to barely more than a third, with 35.5 per cent. That's down from 47.7 per cent five years ago.
Parties on either ideological flank - the Greens on the left, with an estimated 19 per cent, and the Alternative for Germany (AfD) on the far right, with 11 per cent - severely dented the CSU's traditional dominance.
If the results hold, the CSU will need to cut a deal with one or more rivals to stay in power in a state known for its Alpine beauty as well as its industrial might.
The projected results sent a stream of green confetti raining down on jubilant Greens activists at the party's election night headquarters. There was a similarly exuberant celebration among AfD supporters.
It was a different story for the CSU, with a stern-faced Bavarian state premier Markus Soeder telling the party faithful that the result "isn't easy."
"We will accept it with humility. We will need to learn from it. We need to analyse it precisely," he said.
But Soeder insisted that the CSU will continue to lead the state's government, despite a result that is the party's second-worst in its history. The CSU, he said, "isn't only the strongest party, but it received a clear mandate to govern."
The election was closely watched in Germany, and the results appear to fit a pattern seen both within the country and across the continent.
Traditional centrist parties that once flirted with absolute majorities of the vote are withering. Niche and politically extreme parties are gaining as the electorate fragments into ever finer shards.
At the national level, that has meant a record seven parties in the parliament since elections last year, and a deeply dysfunctional governing coalition of three.
Today's result is likely to reverberate loudly in Berlin, where it will be seen as yet another blow to Merkel's once-mighty fusion of her own Christian Democratic Union (CDU) with its Bavarian sister, the CSU.
Since the CDU/CSU faction disappointed in last year's vote, Merkel has seen her authority diminish at home and abroad as she has struggled to cling to a job she has held for 13 years.
Yet the CSU's apparent humiliation could also make Merkel's life easier in one respect: Her primary rival within the government, Interior Minister and CSU leader Horst Seehofer, is likely to face calls to resign.
Seehofer has provoked repeated clashes with his boss this year over immigration, and nearly toppled the Government this year. His defiance of Merkel was widely seen as a deliberate CSU strategy to prove to Bavarian voters that the party could be just as tough on borders and security as its insurgent rivals in the AfD.
But if that was the aim, the effort fell flat. The CSU failed to pry right-wing voters back from the AfD, while more centrist and liberal supporters defected to the progressive-minded Greens.
"People who voted for them for 60 years aren't voting for them anymore. And it's because of their polarising and inhumane politics," said Paul Knoblach, a 12th-generation Bavarian farmer.
Knoblach was among the CSU's longtime supporters and had volunteered for its campaigns. But today, at age 64, he ran for the state parliament for the first time. And he did it as a Green.